Field of the Disclosure
The present application relates to line sensors and associated electronic circuits suitable for sensing radiation at visible, UV, deep UV (DUV), vacuum UV (VUV), extreme UV (EUV) and X-ray wavelengths, and for sensing electrons or other charged particles, and to methods for operating such line sensors. The sensors and circuits are particularly suitable for use in inspection and metrology systems, including those used to inspect and/or measure features on photomasks, reticles, and semiconductor wafers.
Related Art
The integrated circuit industry requires inspection tools with increasingly higher sensitivity to detect ever smaller defects and particles, and requires high precision metrology tools for accurately measuring the dimensions of small features on semiconductor wafers. The semiconductor industry is currently manufacturing semiconductor device with feature dimensions around 20 nm and smaller. Within a few years, the industry will be manufacturing devices with feature dimensions around 5 nm. Particles and defects just a few nm in size can reduce wafer yields, and changes in feature dimensions of a few tenths of 1 nm or less can cause a significant change in the electrical performance, or failure, of a transistor or memory device.
Semiconductor inspection and metrology tools are most useful if they can inspect or measure on all, or most, of the different materials and structures used in CMOS manufacturing. Different materials and structures have very different reflectivities from one another. In order to have the flexibility semiconductor inspection and metrology tools may use multiple wavelengths and/or multiple angles of light illumination and light collection. Selecting which angles to use typically involves switching appropriately shaped and sized apertures into the right location in the optical path according to what is being inspected or measured.
Various inspection and metrology tools of the type related to the present invention are disclosed, for example, in U.S. patent application Ser. No. 14/273,424 (Publication No. 2015/0177159), entitled “A Low-Noise Sensor And An Inspection System Using A Low-Noise Sensor”, and filed on May 8, 2014, U.S. Pat. No. 8,754,972, entitled “High-density digitizer”, issued Jun. 17, 2014, U.S. patent application Ser. No. 14/096,911 (Publication No. 2014/0158864), entitled “Method and apparatus for high speed acquisition of moving images using pulsed illumination”, filed on Dec. 4, 2013, U.S. patent application Ser. No. 13/710,315 (Publication No. 2013/0148112), entitled “Electron-bombarded charge-coupled device and inspection systems using EBCCD detectors”, filed on Dec. 10, 2012, U.S. patent application Ser. No. 13/792,166 (Publication No. 2013/0264481), entitled “Back-illuminated sensor with boron layer”, filed on Mar. 10, 2013, U.S. patent application Ser. No. 13/947,975 (Publication No. 2014/0034816), entitled “Photocathode including silicon substrate with boron layer”, filed on Jul. 22, 2013, U.S. Pat. No. 8,624,971, entitled, “TDI sensor modules with localized driving and signal processing circuitry for high speed inspection”, issued Jan. 7, 2014, U.S. Published Patent Application 2010/0301437, entitled “Anti-reflective coating for sensors suitable for high throughput inspection systems”, filed on Jun. 1, 2009, U.S. Pat. No. 7,609,309, entitled “Continuous clocking of TDI sensors”, issued on Oct. 27, 2009, and U.S. Pat. No. 7,952,633, entitled “Apparatus for continuous clocking of TDI sensors”, issued on May 31, 2011. These applications and patents are incorporated by reference herein.
Apertures are mechanical devices that can occupy significant space. Mechanical motion of apertures can take tens or hundreds of milliseconds, thus slowing inspections or measurements that require data to be collected with more than one aperture. Adding or replacing apertures on an existing inspection or metrology system in order to provide new or improved capability can be difficult owing to space constraints.
Therefore, a need arises for linear sensors having adjustable apertures that facilitate quickly and reliably adjusting the size of each pixel's light sensitive region during operation of an existing inspection or metrology system in a way that overcomes some, or all, of the above-mentioned disadvantages associated with conventional approaches.